1. Technical Field
The inventive concept relates generally to a phase change random access memory device and a method of manufacturing the same and, more particularly, to a phase change random access memory device with a bottom electrode and a method of manufacturing the same.
2. Related Art
Phase-change Random Access Memories (PCRAMs) are memory devices for reading and programming information by changing the state of a phase change materials between a high resistance amorphous state and low resistance crystalline state. PCRAMs offer high operation speeds and high integration degrees. PCRAMs use chalcogenide (GST)-based material which is comprised of germanium (Ge), antimony (Sb) and tellurium (Te) as the phase change material. The chalcogenide is phase-changed between the crystalline state of low resistance, which is a SET state, and the amorphous state of high resistance, which is a RESET state, according to an applied current that is, Joule heat. Whether the stored information is the data “0” of the SET state or the data of “1” of the RESET state is determined by sensing the current flowing through the phase change layer in program and read modes.
Typically, a transistor was used in a conventional PCRAM as a cell switch. Recently, a vertical diode has been investigated for use as a cell switch in an attempt to improve the integration degree and increase the operation current.
A bottom electrode contact (BEC) serves as a heater applying heat to the phase change material in a PCRAM. The large contact resistance between the BEC and the phase change layer on the BEC can maximize the reset current characteristic.
To maximize the reset current characteristic, it is necessary to fabricate the BEC having a diameter of below 40 nm. However, it is difficult to fabricate a contact hole of such a fine diameter by a current lithography apparatus and techniques. Furthermore, if the line width of the BEC is decreased through a double photo lithography process, the area contacted with the phase change layer can reduced so as to ensure the reset current characteristic. However, this reduces the area contacted with the cell switch, and therefore the current transfer characteristic is degraded.